1. Field of the Invention
The invention relates to the field of lighted indicators and in particular to indicators which are particularly adapted for use in combination with night vision goggles.
2. Description of the Prior Art
Night vision goggles are binocular-like device which amplifies low levels of visual or near infrared energy available in typical night time environments to allow the user's vision under starlight to approach that of daytime illumination. Night vision goggles are used extensively in helicopters, aircraft, tanks, troop carriers, combat and landing craft by military, police, and rescue personnel.
It is further long been known in the aeronautic and marine applications to illuminate instrument panels in cockpits or wheelhouses with dim red light. However, night vision goggles are generally saturated by red light so that a pilot wearing a pair of night vision goggles, upon glancing down at the instrument panel, would be subjected to a visual "white-out". This means that the instruments within the vehicle have to be read by a co-pilot who is not wearing night vision goggles, or else the goggle-wearing pilot must lift off or look below the night vision goggles to read the cockpit instruments.
The use of any color other than red will result in a similar vision "white-out" with unaided eyes in attempting to operate in night time environments or create a cabin reflection or glow which can be detected and used as a homing signal for hostile ballistics.
In order to provide cockpit lighting which is compatible both with night vision goggles and unaided vision at night, many techniques have been unsuccessfully attempted. These techniques include spectral separation of the illuminating light relative to the portion spectrums in which the night vision goggles are sensitive. Spectral separation has been accomplished by electro-illuminescent lighting, filters, and the use of frequency specific light emitting diodes. Attempts have also been made to alter the geometry of fixtures of lighted elements to avoid interference. Such fixtures have included such elements as baffles, microlouvers, selected appropriate location of lighting and utilization of controlled reflections. In addition thereto attempts have been made to absorb as much as the nonuseful light in the cockpit as possible through the use of flat black interiors, black flight suits, and antireflection coatings and treatments on all surfaces within the cockpit. None of these prior art attempts have provided a fully satisfactory or practical solution.
Therefore, what is needed is some type of illumination device, particularly adapted for use in indicators or push button switches, which can be compatibly used at night both with unaided vision and by vision aided by night vision goggles.